REFILE-Tennis-Serena powers to second win in Istanbul, Jankovic shines

(Fixes typo in byline)

By Ece Toksabay

ISTANBUL Oct 23 (Reuters) - World number one Serena Williams beat Agnieszka Radwanska for the eighth time in eight matches between them to move ominoulsy towards the semi-finals of the WTA Championships on Wednesday.

The American was again too strong for the Pole in a 6-2 6-4 victory to stay in charge of Red Group with one more round-robin match to come against Petra Kvitova.

Radwanska, who has managed only one set in her meetings with the 32-year-old Williams, is now unlikely to survive the group after two defeats so far at the season-ender.